1. Field of the Invention
The invention relates to an imaging apparatus applied to a video camera in which an optical filter, such as an ND filter, can be selectively arranged. The invention also relates to an imaging method applied in such an imaging apparatus, particularly relating to color-temperature setup technology.
2. Description of the Related Art
Capturing an image using a video camera may require the setting of appropriate color temperature, which can be provided as the basis for an imaging signal. The phrase “setting of color temperature” means that, for example, when capturing an image of a white subject, color temperature is adjusted (corrected) for allowing the white portion of the subject to remain white in a reproduced video image. Color temperature varies depending on whether imaging is carried out under the sun light or under illuminating light. Even in the case of the illuminating light, color temperature varies depending on the kinds of illumination. Also, even in the case of imaging under the sun light, appropriate color temperature may differ depending on the situation of the morning sun or the sunset or the daytime.
The correction of color temperature in a video camera may be optically carried out on imaging light using an optical filter or may be electrically carried out by adjusting a balance of three primary color signals (R, G, B signals) to an appropriate one for an imaging signal obtained by imaging with an image sensor.
Here, an optical filter may be attached to a lens part of the video camera and may be any of neutral density filters (ND filters). The ND filters are used to reduce the amount of light incident on an image sensor. Basically, the ND filters do not alter the color characteristics of light. For example, the ND filter to reduce the amount of light to one fourth (¼), one sixteenth ( 1/16), one sixty fourth ( 1/64), or the like is used.
Such ND filter may be used, for example, outdoors in the daytime to reduce the amount of light, where an image will be captured under very bright environment. Alternatively, when capturing an image indoors, the ND filter may be used depending on the imaging conditions for allowing a user to capture an image under almost full aperture with a shallow depth of field.
Such ND filters may be arranged in different ways. The ND filter may be independent from a camera and manually attached outside on the tip portion of a lens barrel thereof. Alternatively, the ND filter may be previously incorporated in a camera and the arrangement of the built-in ND filter in the light path of the camera can be selectively carried out by a switching operation. In the case of externally mounting a separate ND filter, the filter can be manually attached and removed by the user and such works can be time-consuming. In contrast, in the case of a camera previously incorporating the ND filter, the user can be allowed to select the imaging with the ND filter or the imaging without the ND filter by one-touch switching operation or the like.
Furthermore, in the case of a camera incorporating the ND filter, a plurality of ND filters are incorporated so that these ND filters can be selectively used. In the case of incorporating such a plurality of ND filters, these ND filters are arranged, for example, on a rotating plate provided in the camera at angles with predetermined intervals. Thus, the filters can be selected by the setting of the rotational angle position of the rotating plate.
Also, color-compensating filters (CC filters) that carry out the color temperature correction as described above may be assembled into a similar kind of rotating plate in a video camera as described above. Thus, temperature correction for two or more kinds of color can be optically carried out by setting the rotational angle position of the rotating plate.
Japanese Unexamined Patent Application Publication No. H05-137147 describes an example of a video camera that is capable of carrying out color temperature correction.